PORTLAND LIMESTONE CEMENT

SEMINAR REPORT

MASTER OF TECHNOLOGY

IN

CIVIL ENGINEERING

(STRUCTURAL ENGINEERING AND CONSTRUCTION MANAGEMENT)

Submitted by

NAJEEB.M

(Reg No. 84113)

DEPARTMENT OF CIVIL ENGINEERING

MAR ATHANASIUS COLLEGE OF ENGINEERING

KOTHAMANGALAM 686 666

JUNE 2014

MAR ATHANASIUS COLLEGE OF ENGINEERING KOTHAMANGALAM 686 666

DEPARTMENT OF CIVIL ENGINEERING

CERTIFICATE

This is to certify that the seminar report on Portland Limestone Cement is a

bonafide record of the seminar presented by Najeeb.M (Reg No. 84113) in partial

fulfilment for the award of the degree of Master of Technology in Civil Engineering

with specialisation in Structural Engineering and Construction Management

Prof. Jayasree Ramanujan Dr. Laju Kottalil Prof. Mercy Joseph Poweth

(Staff Advisor) (P. G. Coordinator) (Head of the Department)

i

ACKNOWLEDGEMENT

I express my deep and sincere gratitude to my guide, Smt. Jayasree Ramanujan,

Professor, Department of Civil Engineering, for the kind co-operation and guidance for the

completion of my seminar.

I also extend my gratitude to P. G. Coordinator Dr. Laju Kottalil, Professor,

Department of Civil Engineering, and Prof. Mercy Joseph Poweth, Head of Department,

Civil Engineering and all staff members for the valuable support they offered to me.

I thankfully acknowledge my parents, my friends and all others who have helped

me directly or indirectly for the successful completion of this seminar.

Last but not the least I thank The Almighty, for giving me the strength and power

to conduct this seminar.

NAJEEB.M

ii

ABSTRACT

Portland-limestone cements (PLC) have been used in practice for a considerable

period of time in several countries. In 2008, the CSA A3000 cements committee approved

the addition of a new class of cement with up to 15% interground limestone.

The main advantage of producing Portland-limestone cement is its contribution

to sustainable development. By introducing limestone into cement, the total volume of

cement would increase, or in other words, the amount of clinker required to produce a

certain amount of cement would decrease. This would result in a substantial amount of

energy saving in the production of cement as the consumption of natural raw materials

and the fuel needed for production of clinker would be reduced. Moreover, it would

contribute to sustainable development due to the reduction in greenhouse gas emissions,

mostly CO2 and NOx, involved in the pyro processing of clinker. On this basis, the future

world production of Portland-limestone cement is expected to increase. Nevertheless, it

should be noted that all the aforementioned benefits can only be achieved provided that

Portland-limestone cement has similar performance characteristics to Portland cement,

and has no adverse effects on the properties of concrete.

The properties of Portland-limestone cements have been the subject of numerous

studies. Researchers have studied the effect of using Portland-limestone cement with

various limestone contents on fresh properties, mechanical properties, and durability of

concrete.

This seminar paper covers a brief introduction to Portland Limestone Cement, its

properties, equivalent strength, equivalent durability and Shrinkage properties

iii

CONTENTS

SL No TITLE PAGE No.

ACKNOWLEDGEMENT i

ABSTRACT ii

LIST OF TABLES iv

LIST OF FIGURES v

1 INTRODUCTION 1

1.1 Initiatives 1

1.2 Portland-Limestone Cements 2

1.2.1 History 3

1.2.2 Current Situation 6

1.2.3 Production of Portland Limestone Cement 7

2 PROPERTIES OF PORTLAND LIMESTONE CEMENT 8

2.1 Effects of PLC on Concrete 9

3 EQUIVALENT DURABILITY PERFORMANCE OF 10

PORTLAND LIMESTONE CEMENT

3.1 Alkali-Silica Reaction 11

3.2 Sulphate Resistance 13

3.3 Freezing-and-Thawing and Scaling Resistance 15

3.4 Carbonation 17

4 EQUIVALENT STRENGTH OF PORTLAND 19

LIMESTONE CEMENT

4.1 Materials, Testing, and Results 20

4.2Mechanisms Involved in Equivalent Strength 22

5 EARLY-AGE SHRINKAGE BEHAVIOR OF 25

PORTLAND LIMESTONE CEMENT

5.1 Shrinkage Studies 25

5.2 Chemical Shrinkage 26

5.3 Shrinkage and Cracking 27

6 CONCLUSION 30

REFERENCES 31

iv

LIST OF TABLES

Sl No. NAME OF TABLES PAGE No.

Table 1 Typical Properties of PLC 9

Table 2 Results of freezing-and-thawing tests 16

(ASTM C666/C666M, Procedure A)

Table 3 Typical PC and targets for PLC 20

Table 4 Characteristics of produced cements 20

Table 5 Mixture design used for concrete testing 22

Table 6 Concrete Test Results 22

Table 7 Estimation of reacted cement for the three different systems 24

v

LIST OF FIGURES

Sl No NAME OF FIGURES PAGE NO

Fig 1 CEN Data on types of cement produced in Europe 5

Fig 2 Example fineness trends PLC vs. clinker and limestone 7

component fractions

Fig 3 Concrete prisms stored for 2 years over water at 38C (100F) 12

Fig 4 Mortar bars immersed for 14 days in NaOH solution at 80C 13

Fig 5 Mortar bars immersed for 28 days in NaOH solution at 80C 13

Fig 6 Control mixtures and mixtures with fly ash 14

Fig 7 Control mixtures and mixtures with slag cement 15

Fig 8 Scaling mass loss per ASTM C672/C672M 18

Fig 9 Depth of carbonation of concrete prisms after 2 years 18

Fig 10 ASTM C109 mortar cube strength results 21

Fig 11 Illustration of the simple hydration model used 23

Fig 12 Chemical shrinkage plots of OPC, PLC, and PLC-Slag 27

mortars at w/b of: (a) 0.39 and (b) 0.34

Fig 13 Autogenous shrinkage measurements for OPC, PLC, and 28

PLC-Slag systems with w/b of: (a) 0.39; and (b) 0.34

Fig 14 Stress development in the dual-ring tests of mortar 29

specimens with w/b values of 0.34

Fig 15 Age of cracking in the single ring tests 29

1

1. INTRODUCTION

1.1. Initiatives

Concrete is the second most consumed material in the world after water. It is

estimated that approximately 10 km3 of concrete is required annually, which corresponds

to about 1.5 m3 per person. Ordinary concrete typically contains about 12% cement.

Currently, Portland cement is the most common type of cement used to bond concrete

in many parts of the world. Recent statistics indicate that about 3 billion tons of cement

is produced every year.

The main component of Portland cement is ground clinker, which mainly consists

of calcium silicates, with some aluminum- and iron-containing phases. Clinker is

manufactured by mixing limestone (calcium source), clay (silica and alumina sources)

and iron ore in a rotary kiln and heating the mix to over 1450 C. This high temperature,

which is usually reached by burning fossil fuels, leads to chemical reactions that transform

raw materials into clinker. This results in large emission of greenhouse gases, especially

carbon dioxide, both from the burning of fossil fuels and from decalcification of limestone.

It is often stated that the production of 1 ton of cement results in emission of 0.8

ton of CO2. In fact, estimations show that the manufacture of Portland cement is

responsible for between 5 to 8% of global CO2 emissions. In fact, production of cement

is expected to further increase because of the exponential growth rates in developing

countries, such as China and India, which are the major cement producers and consumers

in the world. Therefore, it is imperative that steps be taken in order to reduce the CO2 released into the atmosphere. This involves either incorporating new environmentally

friendly manufacturing technologies or finding substitute materials to replace a major

part of Portland cement for use in concrete industry. Due to the limitations involved in

reducing CO2 emissions from alternative raw materials and fuels or by improving kiln

efficiency, the first option seems to be not practical. Hence, probably the most effective

means of achieving significant reductions in CO2 emissions lies in the replacement of

Portland cement by other suitable materials, or alternatively by reducing the clinker

component of Portland cement.

Replacement materials that react with calcium hydroxide are commonly known as

Supplementary Cementitious Materials (SCMs). They include fly ash, ground

2

granulated blast furnace slag (GGBFS), pozzolans, silica fume, metakaolin, etc. These

replacement materials can be added separately to the concrete, allowing a reduction in the

cement content of concrete, or used to replace the clinker in blended/composite cements.

Blended cements, i.e. cements comprising of supplementary cementitious

materials such as ground granulated blast furnace slag, fly ash, pozzolans, and silica

fume, are being produced by many cement manufacturers, and are used extensively in the

concrete sector. According to Mehta (2007), the use of supplementary cementitious

materials has increased from 10% in 1990 to about 15% in 2005, and it is viable to

increase this number to about 50% in 2020. SCMs are beneficial not only in the sense

that they contribute to sustainability and reduction in CO2 emissions, but also due to the

potential ability of these materials to enhance the properties and performance of concrete.

In addition to that, some of the SCMs such as slag and fly ash are byproducts of other

industries, and their use could help preserve non-renewable resources.

1.2. Portland-Limestone Cements

One of the materials that has been introduced to Portland and blended cements as

a constituent is limestone or calcium carbonate (CaCO3). This has led to the production

of Portland-limestone cement, i.e. cements that have been interground with limestone.

Most Portland cement specifications allow the use of up to 5% limestone. Beyond that,

Portland-limestone cements are categorized based on the percentage of limestone added

to the cement. Portland-limestone cements consisting of limestone from 5% up to about

40% are being produced and used in various countries around the world, with the most

commonly used cement type in Europe being CEM II/A composite cement with 5-20%

limestone. Also, different standards have stated specifications with regards to the amount

of limestone used in Portland-limestone cements. In 2008, CSA A3001 adopted a new

class of Portland-limestone cements with up to 15% interground limestone.

Perhaps the main advantage of producing Portland-limestone cement is its

contribution to sustainable development. By introducing limestone into cement, the total

volume of cement would increase, or in other words, the amount of clinker required to

produce a certain amount of cement would decrease. This would result in a substantial

amount of energy saving in the production of cement as the consumption of natural raw

materials and the fuel needed for production of clinker would be reduced. Moreover, it

would contribute to sustainable development due to the reduction in greenhouse gas

3

emissions, mostly CO2 and NOx, involved in the pyro processing of clinker. On this basis,

the future world production of Portland-limestone cement is expected to increase.

Nevertheless, it should be noted that all the aforementioned benefits can only be achieved

provided that Portland-limestone cement has similar performance characteristics to

Portland cement, and has no adverse effects on the properties of concrete.

The properties of Portland-limestone cements have been the subject of numerous

studies. Researchers have studied the effect of using Portland-limestone cement with

various limestone contents on fresh properties, mechanical properties, and durability of

concrete. Overall, the data found in the literature seems to be inconsistent in some

specific areas, especially in cases where the limestone content of Portland-limestone

cement is greater than 5%. Data reported in the literature is apparently affected by the

quality and particle size distribution of the limestone used. Also whether the limestone

was interground, blended, or added at the mixer seems to have an influence on the results.

Hence, it is important that these factors be taken into consideration when interpreting the

data.

1.2.1. History

The use of Portland-limestone cements has been in practice for a considerable

period of time in several countries. It seems that European countries have been the

leaders in producing and using Portland-limestone cement. According to Schmidt (1992),

Heidelberg Cement, the main cement producer in Germany, used to produce an energy-

saving cement which contained 20% interground limestone and was used for special

applications as early as 1965. In 1979, a new standard introduced in France permitted the

incorporation of up to 35% of slag, fly ash, natural or artificial pozzolans, and limestone

in a new type of cement called CPJ.

Later on, a specific cement designated as PKZ which consisted of 85+/-5%

clinker and 15+/-5% limestone was specified in the 1987 draft of the European standard

EN 197 (Schmidt 1992). This type of Portland-limestone cement, along with other types

of blended cements, was reported to be commonly used throughout Germany by 1990. In

addition to that, the British Standard BS 7583 allowed use of up to 20% limestone in

cement in the United Kingdom in 1992 (Schmidt 1992). However, the use of it did not

become so popular until the concrete standard BS 5328 was amended in 1997 to include

its use in concrete. Nonetheless, the standard prohibited the use Portland- limestone

4

cements in conditions of freezing/thawing and exposure to sulfates.

In the current version of the European standard EN 197-1 (2000), all of the 27

common types of cement recognized by the standard are allowed to contain up to 5%

minor additional constituents (MAC), the most typical of which are limestone and cement

raw meal. Moreover, four of the designated 27 types correspond to Portland-limestone

cements which allow higher amounts of limestone in two replacement level ranges,

namely CEM II/A-L and CEM II/A-LL with 6 to 20% limestone, as well as CEM II/B-L

and CEM II/B-LL with 21 to 35% limestone in addition to the 5% MAC. It should be

noted that based on different qualities of the limestone used, the Portland-limestone

cements are designated as L and LL. Type LL restricts the total organic carbon (TOC)

to less than 0.20% by mass while Type L restricts the TOC to 0.50% by mass. However,

for both L and LL designations, the calcium carbonate content is greater than 75% and

the clay content is less than 1.20g/100g. Adopted from a study (Sprung and Siebel, 1991),

these purity requirements are selected to minimize the risk of poor performance of non-

air-entrained concrete in freezing/thawing exposures.

According to the Cement Standards of the World (CEMBUREAU 1991), more

than 25 countries allow the use of 1% to 5% limestone in their P (Portland) cements.

Also, many countries allow up to 35% replacement in PB (Portland composite) cements.

According to Hawkins et al. (2005), several countries have modified their standards

to permit limestone in some amount, including Australia, Italy, New Zealand, and the

United Kingdom since 1991. Taken from the latest edition of Cement Standards of the

World, Figure 1 represents how the production of Portland-limestone cement has been

increasing over time in recent years in Europe. The graph shows that the use of CEM

II limestone cements has grown from 15% in 1999 to 31.4% in 2004 and became the

single largest type of cement produced in Europe. As well, most CEM II composite

cements contain limestone.

5

Fig 1. CEN Data on types of cement produced in Europe

Portland cements with some level of interground limestone have been in use in

North American countries as well. However, compared to Europe, the use of Portland-

limestone cements in North America is relatively new and limited. In the US, ASTM C

150 allowed up to 5% limestone to be used in all types Portland cements in 2004. In

Canada, the use of up to 5% ground limestone in Type 10 Portland cement (Type GU in

the new standard) has been permitted in the Canadian cement standard CSA A5 (now

A3001) since 1983. In 1998, the CSA standard allowed the use of up to 5% limestone in

all different types of Portland cement, and this was reaffirmed in 2003. It was not until

2006 that the concept of allowing higher levels of limestone in cements was raised at the

CSA meeting (Hooton et al, 2010). Prior to any modifications to the standard, a

comprehensive literature review was undertaken to review the use of Portland-limestone

cements (Hooton et al, 2007). Besides pointing out that limestone cements had been used

in European countries since the 1960s and that they are now the most commonly used

cements in the European Union, the authors concluded that the technical data supported

the addition of up to 15% limestone. In 2008, the CSA A3000 cements committee

approved the addition of a new class of cement, designated as Portland-Limestone Cements

(PLC), with up to 15% interground limestone. The CSA A23.1 concrete committee also

6

approved the use of PLC in concrete in 2009, and it was included in the National Building

Code of Canada in 2010 as well as several provincial building codes.

1.2.2. Current Situation

As mentioned before, there are four classes of composite cements with limestone

filler in the European Standard, namely CEM II/A-L or-LL (6-20% limestone) and

CEMII/B-L or -LL (21-35% limestone). It is interesting that except in Sweden and Italy,

none of these types of cement are allowed to be specified where sulfate resistance is

required (CEN, 2003). In Sweden, testing for sulfate resistance must be performed, and in

Italy, there are certain restrictions on the C3A content of the clinker and the severity of

sulfate environment. This fact reflects the concern over performance of Portland-

limestone cements in sulfate exposures.

The literature review on Portland-limestone cements (Hooton et al, 2007)

suggested that the literature was conflicting with respect to use of Portland-limestone

cements in sulfate exposures. They pointed out inconsistencies in the trends found by

different researchers as to whether limestone improved or worsened sulfate resistance of

cement, either for conventional sulfate attack or in regards with thaumasite related

deterioration. Moreover, data on the performance of Portland-limestone cements when

used in conjunction with SCMs is limited. The recommendation was that more work

needs to be done in the Canadian context (e.g. at CSA exposure levels and sulfate types)

on the performance of Portland-limestone cements at both 5C and 23C. This should

include use of plain Portland-limestone cement and its combination with levels of SCMs

currently known to provide good sulfate resistance as well as on CSA MS and HS

cements.

Due to this uncertainty about the performance of Portland-limestone cements in

sulfate environments, their use was not allowed in sulfate exposures in the 2008 revision

until further research had been conducted. By that time, the cement companies had

started trial grinds and testing the properties of Portland-limestone cement had been

initiated. However, the concern over the sulfate resistance of Portland-limestone cements,

especially in regards with thaumasite sulfate attack, became the driving force behind

several research studies. Based on the result of this research, including the present study,

the 2010 version of the CSA A3001 standard stated that Portland-limestone cements may

be used in sulfate environments provided that they are combined with the specified

7

minimum percentages of supplementary cementing materials and tested for sulfate

resistance at both 5C and 23C. According to the standard, Type MSLb (moderate-

sulfate resistant Portland-limestone) and HSLb (high-sulfate resistant Portland-limestone)

cements shall contain a minimum of 25% Type F fly ash or 40% slag or 15% metakaolin

or a combination of 5% Type SF silica fume with 25% slag or a combination of 5% Type

SF silica fume with 20% Type F fly ash However, these changes have not been adopted

by CSA A23.1 yet.

1.2.3. Production of Portland Limestone Cement

A metered proportion of crushed, dried limestone is fed to the finish grinding mill

along with clinker and gypsum. The limestone is more easily ground than the clinker

(which is harder) and becomes concentrated in the finest particles. Overall fineness must

be higher (for equivalent performance) in order for fineness of the clinker fraction to be

similar to OPC. Because of this, Production rate is slowed and some additional grinding

energy is required but is more than offset by lower clinker content and related kiln fuel

savings.

Due to addition of limestone and grinding it along with clinker, Particle size

distribution is enhanced and hydration is enhanced by both physical and chemical

interaction; greater overall cementitious efficiency is possible. Sustainability benefits are

significant via reduced associated carbon emissions and embodied energy (less clinker.

Fig 2. Example fineness trends PLC vs. clinker and limestone component fractions

8

2. PROPERTIES OF PORTLAND LIMESTONE CEMENT

Optimum performance in terms of strength and durability is achieved in concrete

when the water content is kept as low as possible, consistent with ensuring satisfactory

placing and thorough compaction.

Other factors affecting performance include conditions of curing as well as the

individual properties of the constituent materials and their proportions in the mix. The

potential performance of any Portland cement based product will only be best developed

under saturated conditions. Appropriate curing is necessary for optimum performance.

Loss of any water to the surroundings should be guarded against and for a period of at least

seven days precautions should be taken to keep the concrete moist and to prevent premature

drying. The rate of strength development will depend on ambient conditions and the initial

temperature of the mix. As a general rule, concrete should be placed within the range of

10C to 30C. In cold weather, freshly poured concrete should be protected against frost to

avoid damage.

At higher temperatures concrete should be protected to avoid increased risk of loss

of water by evaporation, which may lead to cracking caused by drying shrinkage and

thermal stresses, and reduced ultimate performance and strength.

9

Table 1. Typical Properties of PLC

Filler Content 6-20 %

Bulk Density Fresh Blown 900-1100 kg/m3

Settled 1100-1350 kg/m3 Compacted 1350-1450 kg/m3

Chemistry (Main Oxides)

CaO 60-70 % SiO2 15-25 %

Al2O3 3-5 % Fe2O3 2.0-3.5 %

MgO 0.5-1.5 % Sulphate SO3 Less than 3.5% Chloride Cl Less than 0.05% Declared Mean Alkali Na2Oeq Less than 0.75% Colour Tri-stimulus Y 25-40 Surface Area 350-550 m2/kg Setting Time 100-200 minutes Strengths 2 days 15-30 MPa 7 days 20-45 MPa 28 days 40-60 MPa

2.1. Effects of PLC on Concrete

Effects of PLC on Fresh concrete are all favorable (though slight). There is no

difference in water demand, slump loss, when PLC used. Also excellent finishing

properties are obtained for PLC. Generally no change for straight cement systems in case

of the setting conditions. Response to admixtures are similar to that of normal concrete.

Strength development is at least equivalent, though both rate of strength gain and ultimate

strength may be enhanced, especially in combination with SCMs. Shrinkage, heat of

hydration, and durability performance attributes all similar or even slightly improved.

10

3. EQUIVALENT DURABILITY PERFORMANCE OF PORTLAND LIMESTONE CEMENT

The approach to introducing PLC into specifications has varied. In Europe, PLC is

designated as a CEM II cement (CEM I is PC) and is further divided into CEM II/A or

CEM II/B, respectively for cements with 6 to 20% or 21 to 35% limestone. ASTM

International includes PLC in the specification for blended cements, ASTM C595/C595M,

Standard Specification for Blended Hydraulic Cements, as Type IL, with the same

physical requirements (for example, mortar strength) as for Type IP (Portland pozzolans

cement) or Type IS (Portland-blast-furnace slag cement)with no more than 70% slag

cement. Limestone is also permitted as a component of cements produced in accordance

with ASTM C1157/C1157M, Standard Performance Specification for Hydraulic

Cement. In Canada, PLC is covered by CSA A3001, Cementitious Materials for Use in

Concrete, and the performance requirements are identical to those for PC. Contrary to the

European standards for cement, the ASTM and CSA specifications both limit the quantity

of limestone in PLC to 15%.

The approach has been to produce PLC such that it has equivalent performance

to PC (concrete produced with the PLC will have the same strength and durability

properties as concrete produced with PC manufactured from the same clinker) and can,

consequently, replace PC in all applications with no detriment to constructability, strength,

or durability. It is shown in a companion paper that equivalent strength is achieved by

grinding PLC to a higher fineness than PC produced from the same clinker. Before PLC

was adopted by CSA, a comprehensive test program was conducted to demonstrate that the

durability of concrete produced with PLC was also equivalent to that of concrete

produced with PC of the same strength. However, a few concerns remain regarding the

universal transition from PC to PLC.

In many locations, blends of PC and supplementary cementitious materials (SCMs) are used as alternatives to low-alkali PC and sulfate-resistant PC to provide

resistance to alkali-silica reaction (ASR) and sulfate attack, respectively. However,

there are currently few data available on the performance of PLC-SCM blends with

regard to ASR and sulfate attack;

It has been adequately demonstrated that properly proportioned concrete produced with PLC is resistant to cyclic freezing and thawing and to deicer salt scaling.

11

However, there has been little research to show whether PLC concrete is as robust

as PC concrete in less-than- ideal situations, such as when poor construction

practices lead to increased water contents or improper finishing. Concrete produced

with PLC-SCM blends and a high water-cementitious material ratio (w/cm) may be

more vulnerable than similar concrete made with PC-SCM blends; and

Published research on the carbonation of concrete is ambiguous. The rate of carbonation of concretes produced at the same w/cm increases with the amount of

limestone in the cement. However, the PLC and PC used in these studies were not

manufactured to produce equivalent strength. PC and PLC concretes proportioned

to achieve equivalent 28-day strength have about the same rate of carbonation;

however, the PLC concrete was proportioned with a lower w/cm than the PC

concrete to achieve equivalent strength. There are no published carbonation data

related to the performance of concrete with PLC that has been ground to produce

equivalent strength as PC at the same w/cm. Additionally, there is little information

on the carbonation of PLC with relatively high amounts of SCMs. High levels of

SCMs are known to render concrete more susceptible to carbonation.

Research results presented in this article address these unresolved issues. For each

study included here, PC and PLC came from the same mill circuit, the target limestone

content of the PLC was 12%, the limestone was inter- ground with the cement clinker,

and the fineness of the PLC was increased to achieve the same 28-day (mortar) strength as

the PC.

3.1. Alkali-Silica Reaction

It is well established that most types of SCMs can be used to control expansion due

to ASR, provided that the SCM is used at a sufficient level of replacement. However, there

is some controversy over the best test method for determining the amount of SCMs

required. Although the concrete prism test (ASTM C1293, Standard Test Method for

Determination of Length Change of Concrete Due to Alkali-Silica Reaction) is considered

by some to be the most reliable it requires a 2-year test duration. The accelerated mortar-

bar test (ASTM C1567, Standard Test Method for Determining the Potential Alkali-Silica

Reactivity of Combinations of Cementitious Materials and Aggregate (Accelerated

Mortar-Bar Method)) is thus being more commonly selected for evaluating preventative

measures, as it allows a much shorter exposure of the mortar bars to the test solution.

12

However, there is no universal agreement regarding the appropriate duration of exposure

some specifications require 14 days and others require 28 days.

Figure below shows expansion results for the concrete prism test after 2-year

storage over water at 38C (100F) and for mortar bars after 14- or 28-day immersion in a

1 M NaOH solution at 80C (176F). Concrete and mortar bars were produced with a

reactive siliceous limestone (Spratt), and either PC or PLC. Various levels of cement

replacement, with either Class F fly ash or slag cement, were used. The data show that the

expansion levels for PC and PLC mixtures are almost identical for mixtures with the same

SCM and replacement level. Mixtures with SCM exhibit profoundly lower expansion than

the control mixtures, and the efficacy of cement replacement with Class F fly ash or slag

cement does not appear to be significantly influenced by the presence of 12% limestone in

the cement.

Fig 3. Concrete prisms stored for 2 years over water at 38C (100F)

13

Fig 4. Mortar bars immersed for 14 days in an NaOH solution at 80C

Fig 5. Mortar bars immersed for 28 days in an NaOH solution at 80C

3.2. Sulfate Resistance

Various precautions are required if concrete is to be exposed to sulfates during

service. For example, ACI 318-118 imposes restrictions on the w/cm, strength, and type of

cement to be used. For the most aggressive exposure conditions, ACI 318 requires the use

of sulfate-resisting portland or blended cements combined with a pozzolan, slag cement,

or both. Alternatively, any blend of cementitious materials can be used provided it can be

demonstrated that expansion of mortar bars produced with that material does not exceed

14

0.10% after 18-month immersion testing in a solution of 5% Na2SO4 (ASTM C1012/

C1012M, Standard Test Method for Length Change of Hydraulic-Cement Mortars

Exposed to a Sulfate Solution.)

Figure below shows the expansion results for various PLC-SCM and PC-SCM

combinations tested in accordance with ASTM C1012. The clinker used to produce the

PLC and PC has a moderate to high C3A content and, as such, the cements are not expected

to be sulfate resistant when tested without SCMs. This is clearly demonstrated by the rapid

expansion of the control mixtures. The expansion data reveal that cement replacement with

either 15% fly ash or 40% slag cement is sufficient to reduce the 18-month expansion to

less than 0.10%, but replacement with 20% slag cement is not sufficient to meet the 18-

month limit. Whether PC or PLC is used does not appear to have an impact on the outcome

of the test.

Fig 6. Control mixtures and mixtures with fly ash

15

Fig 7. Control mixtures and mixtures with slag cement

There is conflicting evidence regarding the performance of PLC concrete mixtures

exposed to conditions that increase the likelihood of the formation of thaumasite (sulfate

exposure at temperatures of 5C [40F]).2 Preliminary findings have indicated, however,

that the limestone content does not appear to have a significant influence, at least for

cements containing up to 15% limestone. Recent studies reported indicate that for cement-

SCM systems containing an insufficient amount of SCM (30% slag cement in their study),

additional performance requirements sulfate expansion tests at 5C when PLC is to be used

in sulfate exposure.

3.3. Freezing-and-Thawing and Scaling Resistance

Cyclic freezing-and-thawing tests (ASTM C666/C666M, Standard Test Method for

Resistance of Concrete to Rapid Freezing and Thawing, Procedure A) were conducted on

concrete mixtures with high w/cm (0.74, 0.80, and 0.90) and blends of PC or PLC with

SCMs. The w/cm values are above the maximum values specified in the Canadian

Specification (CSA A23.1-09, Concrete Materials and Methods of Concrete

Construction), which are 0.55 or 0.50, respectively, for concrete exposed to freezing and

thawing in an unsaturated or saturated condition. The increased w/cm values were selected

to compare the robustness of concrete produced with PLC-SCM blends with that of

concrete produced with PC-SCM blends; the authors do not endorse the use of the rate of

deterioration increases and time to failure decreases with increasing amounts of limestone

16

(up to 22%). However, provided a sufficient level of SCM is used (50% slag cement in the

study), satisfactory performance is achieved irrespective of the limestone content up to

22%. Note. the CSA specifications prescribe minimum SCM replacement levels and

impose these higher w/cm values for concrete exposed to freezing and thawing. All

concretes were air-entrained with a target air content of 6%. Table 2 shows the results after

300 freezing-and- thawing cycles. Satisfactory durability factors (>90%) and small length

changes were observed for all mixtures regardless of w/cm, type of cement (PC or PLC),

or type and presence of SCM (fly ash or slag cement). All specimens exhibited mass loss

from the surface after 300 cycles. While the mass loss increased with increasing w/cm, it

was not significantly influenced by the type of cement or SCM used.

Table 2. Results of freezing-and-thawing tests (ASTM C666/C666M, Procedure A)

w/cm Property Control 20% Fly Ash 35% Slag Cement

PC PLC PC PLC PC PLC 0.74 Durability factor % 99 100 100 100 95 97

Length increase, m/m 28 24 12 8 10 8Mass loss, % 4.43 4.11 2.88 3.63 3.17 2.45

0.80 Durability factor % 98 99 95 99 95 96 Length increase, m/m 24 22 27 7 5 42

Mass loss, % 4.43 5.11 6.09 5.39 4.81 4.25 0.90 Durability factor % 99 94 95 100 96 96

Length increase, m/m 22 22 17 7 10 7 Mass loss, % 5.56 9.93 9.40 9.74 4.43 5.18

Deicer salt scaling tests (ASTM C672/C672M, Standard Test Method for Scaling

Resistance of Concrete Surfaces Exposed to Deicing Chemicals) were conducted on

concrete mixtures with w/cm of 0.45, 0.50, and 0.55 and PC or PLC, with or without SCM

(fly ash or slag cement). The Canadian Specification (CSA A23.1-09) imposes a maximum

w/cm of 0.45 for concrete exposed to freezing and thawing in the presence of deicing salts.

Again, the increased values were selected to test the robustness of the PLC-SCM blends;

the authors recommend compliance with the CSA limit for concrete exposed to freezing

and thawing and deicing chemicals. Figure 3 shows the mass loss of concrete samples after

50 freezing-and-thawing cycles. The data show that the extent of scaling is dependent on

both the w/cm and the presence of SCM. The data also show that there is little significant

influence of the cement type (PC or PLC), although PLC mixtures with higher w/cm and

25% fly ash exhibited the most scaling.

17

The data in Figure are for slabs that were finished after bleeding and then moist-

cured for 14 days and air-dried for 14 days prior to exposure to freezing-and-thawing

cycles; this is a standard procedure set forth in ASTM C672/ C672M. Tests were also

conducted on slabs for which the standard procedure was modified; the modifications

included finishing immediately after striking off the concrete (before bleeding) and

shortening the air-drying period to 2 days. These modifications had a marginal impact on

the outcome of the test and the results were not significantly influenced by the use of PLC

compared with PC.

Concrete slabs (600 x 600 x 150 mm [24 x 24 x 6 in.]) were cast using the same

mixture proportions as those used for the laboratory scaling tests. The slabs were cast

outdoors (in southeast Ontario) and treated with a curing compound after finishing. Deicing

salt (predominantly NaCl) is applied regularly to the surface of these slabs during winter

months and the slabs are exposed to numerous freezing- and-thawing cycles per year.

Figure 4 shows the surface appearance of slabs (with the highest w/cm of 0.55) after two

winters of service. There has been minor scaling of all of the slabs at this w/cm but neither

the cement type (PC versus PLC) or the presence of SCMs (25% fly ash or 35% slag

cement) appears to have significantly influenced the scaling. The slabs produced at lower

w/cm are generally exhibiting lesser amounts of scaling.

3.4. Carbonation

Concrete mixtures used for carbonation testing were produced with a w/cm of either

0.45 or 0.55 and with PC or PLC. These cements were used alone or blended with relative

high amounts of SCMs (cement replacements of 40% using fly ash or 60% using slag

cement). Concrete prisms (75 x 75 x 300 mm [3 x 3 x 12 in.]), moist-cured for either 1, 3,

or 7 days, were subsequently stored in air at approximately 55% relative humidity (RH)

and 21C (70F). The depth of carbonation was determined by splitting the prisms at

regular intervals and spraying the freshly-fractured surface with phenolphthalein indicator.

18

Fig 8. Scaling mass loss per ASTM C672/C672M

Figure below shows the results of the carbonation tests after 2 years. As expected,

the depth of carbonation increases with an increase in w/cm, a reduction in the period of

moist curing, and the presence of SCMs. However, there appears to be no influence on

carbonation due to the use of PLC in place of PC.

Fig 9. Depth of carbonation of concrete prisms after 2 years

19

4. EQUIVALENT STRENGTH OF PORTLAND LIMESTONE CEMENT

The equivalent strength performance is a key feature in allowing concrete producers

to have a seamless transition to PLC. However, the manufacturing implications are

noteworthy, as the fineness of the cement (both Blaine and 45 m [No. 325] sieve) must

be significantly increased. Typically, a North American PLC has a Blaine fineness increase

in the range of +8 to +10 m2/kg for every additional percent of limestone compared to its

corresponding PC. For instance, moving from a given PC with 3% limestone to a PLC with

12% limestone would typically correspond to a Blaine fineness increase in the range of

+70 to +90 m2/kg. (Note. ASTM C150/C150M, Standard Specification for Portland

Cement, currently limits the amount of limestone to 5.0% in ordinary PCs. However,

because of other limitations (loss-on-ignition and insoluble residue content), the typical

amount of limestone found in ASTM C150 cements is in the range of 3 %.) This increase

in Blaine fineness results in a decrease in the milling capacity (throughput) and an increase

in the electric consumption used for milling a tons of cement. It is also an indication that

in a PLC, the clinker fraction is ground a little finer than in its corresponding PC to

compensate for the lower clinker content.

The purpose of this article is to demonstrate, with simple analytical techniques and

in a quantitative way, that this increased fineness of PLC is the main driver allowing

equivalent strength. To do this, we have used results obtained during industrial trials

conducted in Canada. The purpose of the trials was to determine the industrial feasibility

of PC-equivalent strength PLC before PLC was fully industrialized. In the trials, PLC

was produced on two different milling circuits from the same raw materials (clinker,

gypsum, and limestone) and was compared to ordinary PC produced on one of these two

milling circuits produced on one of the milling circuits achieved equivalent 28-day

strength, PLC produced on the second milling circuit did not.

The different cement samples produced were separated into five different size

fractions using a classifier that allowed a high-precision size classification without

changing the morphology of particles. The limestone content of the different size fractions

was characterized in order to determine the particle size distribution (PSD) of limestone

and clinker of the different cements. Then, a quantitative analysis was performed to

evaluate to what extent the differences in fineness contribute to the equivalent strength.

20

4.1. Materials, Testing, and Results

Cement production typical limestone content and Blaine fineness for the PC

produced in the plant as well as the targets adopted for the PLC are given in Table.2. The

target was to maintain the calcium sulfate additions constant on a clinker fraction basis (5%

gypsum addition in PC and 4.5% in PLC).

Table 3. Typical PC and targets for PLC

Typical PC PLC Target Limestone, % 3.8 14

Calcium carbonate, % 3.3 12

Blaine fineness, m2/kg 400 490

Blaine fineness increase m2/kg/%L - +9

The PLC was produced during industrial trials on two different milling circuits and

compared to PC. Results from the production trials are reported in Table 3. For PLC1

(produced on Mill Line 1), they are very close to target with a Blaine fineness increase of

+8 m2/kg per percent of additional limestone. However, for PLC2, the limestone content

achieved was too high because of an incorrect setting of the limestone feeding rate to the

mill. As a consequence, although the same overall Blaine fineness increase (+80 m2/kg

compared to the PC) was achieved for both PLC1 and PLC2, the increase for PLC2 only

translates to +6 m2/kg per percent of additional limestone for PLC2. This is significantly

lower than the target of +9 m2/kg per percent of additional limestone.

Table 4. Characteristics of produced cements

Control Line 1 Line 2

Designation PC PLC1 PLC2

Limestone, % 3.6 13.5 16.9

Calcium Carbonate, % 3.2 11.7 14.6 Blaine fineness, m2/kg/%L - +8 +6

Passing 45 m (No. 325) sieve, % 94.4 99.5 92.8

21

The amount passing a 45 m (No. 325) sieve confirms the fineness results, as this

value increased relative to PC for PLC1 but decreased relative to PC for PLC2.

Compressive strength testing ASTM C109/C109M, Standard Test Method for

Compressive Strength of Hydraulic Cement Mortars (Using 2-in. or [50-mm] Cube

Specimens), compressive strength tests on mortar cubes were performed on mixtures

prepared from the three produced cements. Results obtained at 3, 7, and 28 days are

reported in Fig. 10. They confirm that equivalent strength performance is obtained for

PLC1. However, for PLC2, strength results are lower than the control PC by 3.9 MPa (565

psi) at 3 days and 4.9 MPa (710 psi) at 28 days, which represents a strength decrease of

approximately 13% compared to the control PC.

Fig 10. ASTM C109 mortar cube strength results (Note. 1 MPa = 145 psi)

Compressive strength was also measured on concrete prepared according to

Table.5. The results provided in Table6 confirm the PC-equivalent strength for PLC1 and the lower strength of PLC2.

22

Table 5. Mixture design used for concrete testing

Cement, kg/m3 (lb/yd3) 355(598)

5 to 20 mm (No.4 to in.) stone, kg/m3 (lb/yd3) 1080 (1820)

Initial w/c (adjusted for 100mm [4 in.] slump) 0.54

Low-range water-reducing admixture, ml/100 kg (fl oz/100 lb) of cement 195 (3)

Table 6. Concrete Test Results

PC

Average

PLC1

Average

PLC2

Average

Final w/c 0.54 0.56 0.54

Unit weight, kg/m3 (lb/ft3) 2435 (152.0) 2428

(151.6) 2421

(151.1)

Air content, % 1.3 1.1 1.1

Slump, mm (in.) 110 (4.25) 107 (4.25) 108 (4.25)

Setting time, minutes 374 401 386

1-day compressive strength, MPa (psi)

18.0 (2610)

17.1 (2480)

13.5 (1960)

7-day compressive strength, MPa (psi)

32.5 (4710)

31.4 (4550)

27.5 (3990)

28-day compressive strength, MPa (psi)

398 (5770)

39.2 (5690)

35.9 (5210)

4.2. Mechanisms Involved in Equivalent Strength

Even without any consideration for differences in clinker fineness, several

mechanisms have been proposed to explain some of the strength benefits of limestone

cements.

Acceleration and amplification of hydration kinetics due to heterogeneous nucleation sites provided by the surface of fine limestone particles;

23

Formation or stabilization of carbo-aluminates providing additional space-filling hydrates; and

Reduction of the water demand due to a particle packing effect involving the fine limestone grains or as a result of a larger paste content associated with the lower

specific gravity of limestone compared to clinker.

In this work, the objective was to determine to what extent increasing PLC fineness

contributed to the equivalent strength feature. The basics of the model are.

All cement particles are considered to be spheres; All particles are assumed to hydrate with the same kinetics; and The hydrates are assumed to nucleate uniformly at the surface of anhydrous cement

particles.

According to these hypotheses, as illustrated in Fig. 11, at a specific time, the depth

of cement dissolved or reacted (t) is the same for each particle, independent of the particle size. This means at the same point in time, a finer system will have more cement reacted

than a coarser system or a higher degree of hydration.

Fig 11. Illustration of the simple hydration model used

24

If we consider that (28 days) will be about 10 m on every cement particle, the degree of hydration can be estimated for the tested cements as

85% for the control PC; 89% for PLC1; and 84% for PLC2.

It also should be noted that DOH can be calculated for any chosen value of

dissolved depth. The value of 10 m was selected as it corresponds to 85% DOH for a

hydration time of 28 days on the PC sample, which is a typical value.

As the different systems do not have the same clinker content, we apply this DOH

to the clinker fraction of each system to determine the quantity of reacted cement as given

in Table 7.

Table 7. Estimation of reacted cement for the three different systems

Control PC PLC1 PLC2

Limestone, % 3.6 13.5 16.9

Gypsum, % 5.0 4.5 4.5

Clinker, % 91.4 82.0 78.6

DOH at 10 m dissolved, % 85 89 84 Amount of reacted cement, % 78 73 66

It is striking to see that, despite having about 10% less clinker than the control PC,

the PLC1 cement has only 5% less reacted cement than PC. The remaining 5% of the

reaction products can be attributed to the additional mechanisms listed at the beginning of

this section (such as heterogeneous nucleation and formation of carbo-aluminates). But the

results of this simple model are clear. the increased fineness of the clinker portion is a key

mechanism explaining the equivalent strength feature for the conditions investigated in the

present study.

Similarly, the gap in the amount of reacted cement between the control PC cement

and PLC2 is very large because clinker fineness did not compensate for the extra dilution

of clinker content by over dosage of the limestone.

25

5. EARLY-AGE SHRINKAGE BEHAVIOR OF PORTLAND LIMESTONE CEMENT

The primary explanation for the increased shrinkage and cracking with finer cements

revolves around two central arguments. The first is that the finer cement has a higher

surface area, causing the hydration reaction to occur more quickly and leading to a more

rapid gain in stiffness, not providing time for stress to be relaxed out of the system.

The second is that the capillary stress that develops in the pore fluid is greater due to

the smaller pores in mixtures with finer cements (as described by the Young-Laplace

relationship, which states that the capillary stress is inversely related to the radius of the

pore being emptied). It should be noted, however, that when the pores are very large (bigger

than 50 nm), then relatively low stress levels are generated; and when the pores are very

small (smaller than a few nm), the concept of capillary stress due to the formation of a

meniscus loses physical meaning, at which point other mechanisms dominate the shrinkage

behavior.

Previous studies have also examined the shrinkage of cement-limestone blends. The

fineness of the limestone influenced the shrinkage and stress, it should be noted that the

evaluated systems consisted of cement with 10% additions of limestone of various sizes.

As such, the cement limestone blends were not interground and were not designed to have

similar performance (strength). When interground PLC mortar systems with similar

strength were evaluated, the PLC system was shown to have similar or slightly less

shrinkage than the OPC system. The PLC system also had no increased tendency to crack.

The purpose of the current study is to expand upon this work and investigate the potential

risk for shrinkage of interground PLCs containing up to 15% limestone and to better

understand why these engineered PLCs do not appear to exhibit increased shrinkage with

increased Blaine fineness.

5.1. Shrinkage Studies

Shrinkage was evaluated using mortar specimens comprising 55% fine aggregate

by volume and w/b of 0.34 and 0.39. For indirect evaluation of shrinkage using hydration

characterization tests, samples were prepared using graded silica sand complying with

ASTM C778, Standard Specification for Standard Sand, with a specific gravity of

26

2.65 and absorption of less than 0.1%. For direct shrinkage tests, mortar samples were

prepared using river sand with a specific gravity of 2.53 and absorption of 1.8%.

A high-range water-reducing admixture (HRWRA) was used at dosages of 1.2 and

0.6% by weight of binder for mixtures with w/b values of 0.34 and 0.39, respectively.

Indirect estimates of shrinkage were based on the Kelvin-Laplace relationship (that is,

capillary stress is an inverse function of the size of a pore that is emptied by self-desiccation

or external drying). Pore size distributions were estimated by measuring the water

desorption from mortar samples. Hydration rates were based on the results of chemical

shrinkage tests (ASTM 1608-07, Standard Test Method for Chemical Shrinkage of

Hydraulic Cement Paste) conducted at a constant temperature of 23 0.5C (73 1F).

Direct determinations of shrinkage included autogenous shrinkage tests per ASTM

C1698-09, Standard Test Method for Autogenous Strain of Cement Paste and Mortar

length-change tests per ASTM C157/C157M, Standard Test Method for Length Change

of Hardened Hydraulic-Cement Mortar and Concrete; and restrained shrinkage tests, in

which torus-shaped mortar samples were cast in contact with and restrained by

instrumented invar rings. Two restrained shrinkage test methods were used. single-ring

tests were conducted in accordance with ASTM C1581/ C1581M-09, Standard Test

Method for Determining Age at Cracking and Induced Tensile Stress Characteristics of

Mortar and Concrete under Restrained Shrinkage, and dual-ring tests. Ring test

specimens were maintained at a constant temperature and strain measurements were

automatically recorded and used to determine the stress build-up in the mortar samples.

5.2. Chemical Shrinkage

Our chemical shrinkage tests were performed on saturated mortar samples of

approximately 15g (0.53 oz.) and approximately 3 to 6 mm (0.1 to 0.2 in.) tall. Figure 12

shows the chemical shrinkage normalized to the mass of binder up to an age of 1 month.

During the first day, the three mixtures show an insignificant difference, after which point,

the chemical shrinkage of the PLC and PLC-Slag mortars are lower than the OPC. The

chemical shrinkage of the PLC and PLC-Slag mortars were reduced by 6 to 10% and 20 to

24%, with the reduction due to the increasing dilution effect, respectively. It can be noted

that when the chemical shrinkage is normalized by the mass of clinker, the results (not

shown) are nearly identical.

27

Fig 12. Chemical shrinkage plots of OPC, PLC, and PLC-Slag mortars at w/b of.

(a) 0.39 and (b) 0.34

5.3. Shrinkage and Cracking

The autogenous shrinkage from the time of set was measured per ASTM C1698-09.

Results are shown in Fig. 13. The data indicate that shrinkage varied inversely with w/b.

Also, the total shrinkage values for the PLC and OPC mixtures were very similar, but

the PLC-Slag system had slightly lower shrinkage. RH measurements on crushed mortar

samples taken from sealed samples using Rotronic humidity sensors at 23 0.1C (73

0.2F) confirmed this trend in shrinkage (as a function of RH in the pores) with a slightly

lower RH in the OPC system and the highest RH in the PLC-Slag system.

28

Fig 13.Autogenous shrinkage measurements for OPC, PLC, and PLC-Slag systems

with w/b of. (a) 0.39; and (b) 0.34

The PLC and OPC showed similar shrinkage behavior as other PLC systems. This

demonstrated similar shrinkage for other OPC and PLC systems over a wide range of RH

values. Figure 14 shows the stress that developed in the OPC, PLC, and PLC-Slag

specimens during dual-ring tests. While the PLC mixture exhibited a slightly higher initial

expansion, the tensile stresses that developed in all three mixtures were virtually the same.

As the vertical line on the plot indicates, the PLC cracked at a slightly earlier age than the

other specimens, despite having a similar stress level. Similar observations can be made

using results of the ASTM C1581/C1581M test (Fig. 15). It should also be noted that the

age of cracking determined from the ASTM C1581/C1581M test has a relatively high

scatter due to the nature of the test. Figure 15 shows the range of maximum to minimum

measured cracking times in the hashed bars, with one standard deviation from six samples

represented by the horizontal lines over each bar. The results from the single ring tests

indicate slightly earlier cracking ages for the PLC mortars. This difference in cracking age

would be consistent with the PLC having a 5% reduction in tensile strength, based on the

stress level reached when cracking occurred. It should be noted, however, that if a reduction

of tensile strength exists, it appears to be small. The PLC has a slightly higher expansion

29

than the other materials immediately after setting, and this may have contributed to the

observed slight difference in the age of cracking, as the shrinkage subsequent to this

expansion would be higher in the PLC system.

Fig 14. Stress development in the dual-ring tests of mortar specimens with w/b

values of 0.34 (Note. 1 MPa = 145 psi)

Fig 15. Age of cracking in the single ring tests

30

6. CONCLUSION

PLCs have the potential to significantly improve concrete sustainability with

performance equal to or better than C150 / M85 cements, similarly used. PLCs can be

used seamlessly as a substitution for OPCs in mix designs. PLCs hydrate with synergies

contributed by limestone that enable enhanced setting and strength performance, especially

in combination with SCMs. Limestone fineness is a key influence on the extent of synergy

benefits. The particle size distribution of PLC produced to optimum overall fineness in

finish grinding ball mills appears well suited for synergy-driven performance

enhancement.

The performance of PLC concrete will be equivalent to PC concrete provided that

the PLC is ground finer to produce equivalent 28-day (mortar) strength as the PC. Recent

research has shown that combinations of PLC and SCMs can be expected to provide similar

performance in ASR and sulfate attack tests as the same combinations of PC and SCMs.

Further- more, PLC concrete, with or without SCMs, is no less robust than PC concrete in

terms of resistance to freezing and thawing, deicer salt scaling, and carbonation, even when

subjected to poor practices such as the addition of water, improper finishing, and

inadequate curing. This is critical to permit a seamless transition from PC to PLC across

the concrete industry.

It was found that the limestone portion of the PLCs is very fine (>90% finer than

10 m) and that consequently, the Blaine fineness has to be increased significantly to provide clinker that is ground finer. PLC, with an increased fineness of +8 m2/kg per

percent of additional limestone, was found to have a clinker fraction finer than the PC. Its

28-day DOH was estimated to be higher than the 28-day DOH for the PC, and ultimately,

PLC exhibited PC-equivalent strength.

The PLC-Slag system exhibited slightly lower autogenous shrinkage than either the

OPC or the PLC samples. While the three systems developed about the same levels of

restrained shrinkage stress, one of the PLC samples with w/b of 0.39 cracked at a slightly

earlier time. We observed that the slightly earlier age of cracking was consistent with a

measured tensile strength reduction of 5%.

31

REFERENCES

[1] Michael D.A. Thomas, Anik Delagrave, Bruce Blair, and Laurent Barcelo,

Equivalent Durability Performance of Portland Limestone Cement, Concrete

International, December 2013, pp 39-45. [2] Laurent Barcelo, Michael D.A. Thomas, Kevin Cail, Anik Delagrave, and Bruce

Blair, Portland Limestone Cement Equivalent Strength Explained, Concrete

International, November 2013, pp 41-47. [3] Timothy Barrett, Hongfang Sun, Chiara Villani, Laurent Barcelo, and Jason Weiss,

Early-Age Shrinkage Behavior of Portland Limestone Cement, Concrete

International, February 2014, pp 51-57. [4] Gzde _nan Sezer, Oguzhan opuroglu & Kambiz Ramyar, Microstructure of 2 and

28-day cured Portland limestone cement pastes, Indian Journal of Engineering &

Materials Sciences, Vol. 17, August 2010, pp. 289-294 [5] Amir Mohammad Ramezanianpour, Sulfate Resistance and Properties of Portland-

Limestone Cement, Thesis, University of Toronto, 2012

[6] Barcelo, L.; Thomas, M.D.A.; Cail, K.; Delagrave, A.; and Blair, B., Portland

Limestone Cement Equivalent Strength Explained, Concrete International, V. 35,

No. 11, Nov. 2013, pp. 41-47.

[7] Tennis, P.D.; Thomas, M.D.A.; and Weiss, W.J., State-of-the-Art Report on Use of

Limestone in Cements at Levels of up to 15%, SN3148, Portland Cement

Association, Skokie, IL, 2011, 78 pp.

[8] Thomas, M.D.A; Hooton, D.; Cail, K.; Smith, B.A.; de Wal, J.; and Kazanis, K.G.,

Field Trials of Concretes Produced with Portland Limestone Cement, Concrete

International, V. 32, No. 1, Jan. 2010, pp. 35-41.

[9] Hossack, A.; Thomas, M.D.A.; Barcelo, L; Blair, B.; and Delagrave, A.,

Performance of Portland Limestone Cement Concrete Pavements, Concrete

International, V. 36, No. 1, Jan. 2014, pp. 40-45

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